In recent years, so-called pre-package wherein foodstuffs such as vegetables and fruits, fresh fishes, fresh meats and daily dishes with or without a plastic tray for carrying the foodstuffs are stretch-packaged with a film is common practice. Active research is continued to develop, as the film for use in the pre-package, films made of ethylene-series resins such as low-density polyethylene resins, ethylene-vinyl acetate copolymer resins, etc., in place of the conventional films made of poly(vinyl chloride), principally because of safety and hygienic reasons.
However, the films made of low-density polyethylene-series resins such as low-density polyethylene resins, ethylene-butene-1 copolymer resins, etc., which have already been known as films for use in stretch-packaging, are rigid and have low elongation. If the films are stretched with great force, the films will either tear or at most exhibit uneven elongation. In some cases, the tray carrying the foodstuff to be packaged will be deformed or collapse to produce wrinkles in the film and, as a result, such the troubles that the tightening force which is necessary for accomplishing the desired packaging is not attainable or the packaged foodstuff becomes unsaleable are caused.
The films made of ethylene-vinyl acetate copolymer resins are free from the aforementioned troubles of the films made of low-density polyethylene-series resins if factors such as the content of vinyl acetate, the melt flow rate, etc., are properly controlled. However, if the foodstuff to be packaged has sharp corners or if the corners of the tray carrying the foodstuff are sharp, the film made of ethylene-vinyl acetate copolymer resins will tear because of the sharp corners while it is stretched in an attempt to package the foodstuff. In addition, a small tear that may occur in the film if it contacts various objects which are encountered during the distribution of the stretch-packaged foodstuff will propagate either to produce a large tear or to cause the complete unpackaging of the foodstuff.
The troubles of rigidity and low elongation can also be eliminated by laminating the film of low-density polyethylene-series resin with the film of ethylene-vinyl acetate copolymer resin, but the other trouble which is associated with the tear which may occur during packaging operations and in the process of distribution will not be completely solved, particularly when the thickness of the laminated film is comparatively small.
With a view to eliminating the aforementioned troubles of the conventional films for use in the stretch-packaging of foodstuffs and in order to provide a thin film suitable for use in stretch-packaging that has appropriate degrees of lubricity and self-adhesion property and satisfactory levels of heat sealability and transparency and which yet exhibits high degrees of stretchability and flexibility, particularly high tear strength, the present inventors previously invented a film for use in stretch-packaging which comprises a layer that contains a specified propylene-.alpha.-olefin random copolymer resin as its main component and at least two layers each containing as its main component an ethylene-vinyl acetate copolymer resin with a vinyl acetate content ranging from 5 to 25 wt%, the latter layers being laminated over both surfaces of the former layer. (This invention was described in the specification of Japanese Patent Application No. 167566/84.)
This film, however, does not fully satisfy the following requirements of marketability concerning recovery properties from deformation: that the product of interest is tightly packaged with the film and the film provides good fit to the product's shape without producing any wrinkles; and that even if the film is deformed because of the contact with other objects while the packaged product is being transported or displayed at store or in showcases, the film is restored from the deformed state without producing any wrinkles.